Drag of a Laser Trapped Fine Particle in a Microregion

To observe hydrodynamics in microregions, we applied laser scanning manipulation to measure the drag acting on a fine glass bead moving in mineral oil sandwiched between two glass plates (the thickness of the oil layer was a 33 and 64 µm). We measured the maximum velocity, V M, of a laser trapped bead at which the bead was released. This allowed us to quantitatively determine the drag, the drag coefficient, C D, and the Reynolds number, R, of the particle in the microregion of a viscous fluid. As a result, the minimum C D R was obtained midway between the two glass plates, and the C D R increased closer to the walls. Also, the distribution of C D R was in good agreement with the values calculated using the equation for wall effect in macroregions (over 0.1 mm).